The manufacture, supply, and servicing of radio-controlled (R/C) aircraft is estimated to be a multi-million dollar industry in the United States. Itadio transmitters and radio control technology have developed as might be expected in an age of rapid electronic technological growth, yet conventional bellcrank and pushrod linkages are still universally employed in the actuation of R/C engine throttles and other control surfaces. The use of such linkages is well known to result in intermittent and unpredictable binding of controls, leading to partial or total loss of control of the aircraft. They also usually result in loss of range of motion or in lost motion in the controls, leading to lack or loss of precision in control and in lack of precise handling. These same conventional linkages also result in slow and laborious processes for the disconnection, and particularly in reconnection (and necessarily finicky and painstaking readjustment of the linkages) of engines which must be removed for maintenance or repair. Similar problems are encountered in the control of throttles on gasoline-powered lawn mowers and other lawn and garden equipment (the market for which is estimated to equal or exceed that of R/C aircraft) and the like. What is needed is a remote control throttle, and in particular a control linkage, which overcomes these difficulties.
Rotary cables are known for providing power and motion transmission in general, such as for motor governors, and speedometers; however these systems are not known for use in control applications, where torsional stress can be more critical. Power transmission usage of such cables is typically one directional (or if bidirectional, it is still generally continuous and only alternately changes direction). In these conventional applications, strain in the rotary cable is "wound up" or taken up essentially only once for each duty cycle, especially if the rotational speed during the cycle does not vary much.
But in control applications, both speed (or lack thereof, as in no motion at all) and direction of rotation are varied constantly, and the sensitivity and precision losses due to strain wind up or take up can be huge in cables otherwise acceptable in power or motion transmission. A rotary cable for a control system then must partake of the qualities of a flexible shaft, having in particular a substantial torsional strain resistance.
Other proposed control systems cannot endure physical displacement, especially lateral displacement, without changing and affecting the control settings. For example, in a push pull (cable) connection, moving or bending the slack cable or coax has a direct and immediate impact on the control surface to which it is attached. The same is substantially true for bellcrank and pushrod systems.